1. Technical Field
This invention relates to portable vibratory material screening devices and, more particularly, to an improved drive system for portable vibratory material screening devices.
2. Background
Portable vibratory screening devices typically include a supporting frame, heavy duty springs, a screen box with a material separating screen, a drive system and an eccentric shaft. The frame and springs support the screen box and screen for vibratory movement above the ground. The drive system provides torque to rotate the eccentric shaft that is fixedly attached to the screen box.
The eccentric shaft typically includes eccentric weights which cause a dynamic rotational imbalance when the eccentric shaft is rotated. In other words, the eccentric shaft vibrates the screen box when the drive system rotates the eccentric shaft. A loading device such as wheel loaders, skid steers, conveyors or other devices load top soil or other materials to be screened onto the screen box. Because the screen box vibrates, undersize material falls through the screen while oversize material remains on the screen. The screen box is often positioned at an angle relative to the ground to allow the oversize material to vibrate off the screen to make room for additional material to be screened.
The coupling between the output shaft of the drive system and the eccentric shaft has posed several problems. For durability reasons, the drive system must be isolated from the eccentric shaft due to the vibrating movement of the eccentric shaft. Conventional drive system typically utilize a gas or diesel engine or an electric motor that powers a hydraulic pump. Hydraulic hoses and a valve body connect the hydraulic pump to a hydraulic motor that vibrates with the eccentric shaft. While the engine or motor and the hydraulic pump are isolated from the vibration, the hydraulic motor is not. Due to the absence of isolation, the vibration significantly decreases the life of the hydraulic motor. In addition, the hydraulic hoses experience increased failures due to the vibrational fatigue. When these hoses begin leaking, the hydraulic fluid is released causing environmental hazards which can be costly to clean.
Conventional vibratory screening devices also typically require an operator to engage levers or clutches located in the engine compartment during startup engage the drive system. Opening the compartment during startup or while the drive system is operating poses a safety hazard to the operator.
Accordingly, it is an object of the present invention to provide a simple drive system for a vibratory screening plant which eliminates the need for a hydraulic pump, a hydraulic motor and hydraulic hoses. It is another object of the present invention to provide simple drive system and coupling for driving an eccentric shaft. It is yet another object of the present invention to provide a drive system for a vibratory screening device which has a simple starting procedure. These objects and others are achieved by the present invention described hereinafter.